Apologies for bumping this thread but I just found a confirmation that indeed the tannery where Tanner Bates get their Russian Kip leather,
J&FJ Baker, is the one producing Volynka for Hermès.
I don't read French so I'll just post the Google-translated part of
the L'Eperon article about the book,
Cuir de Russie: Mémoire du tan by Sophie Mouquin:
"Elise Blouet, a biologist and restorer of leather and metals, then goes on campaign to
find the recipe of the original Russian leather, that nobody knows ... The investigation of Elise will be long, it will federate the experts of Hermès with researchers in chemistry and historians, craftsmen for a thousand and one tests delicate, uncertain,
until the alliance with tannery Baker in Devon in England... The luxurious brand is also inspired by this adventure since
Hermès uses this tanned leather in England for their new range Volynka leather, available from January"
This is a fascinating video showing how J&FJ Baker tans their hide using centuries-old oak tanning methods, although for Volynka/Russia Kip, a combination of oak, willow, and birch barks is used:
And here one can see how the criss-cross pattern of the Volynka/Russian Kip is achieved by using rollers: